Considerable effort has recently been focused on increasing the immunogenicity of tumors by using gene transfer techniques with the goal of developing useful cellular vaccines for treatment of Cancer. Promising results have been obtained in experimental models in which tumors are engineered to express genes encoding cytokines, costimulatory molecules such as B7, or MHC proteins. However, a number of technical problems may limit the practical utilization of this approach in the clinical setting. An alternative approach is proposed in this application based on immunization with reconstituted tumor membranes containing additional membrane proteins included to increase immunogenicity and the induction of tumor-specific immunity. The first specific aim is to characterize the tumor-specific immune response induced by reconstituted tumor membranes containing additional membrane proteins included to increase immunogenicty and the induction of tumor-specific immunity. The first specific aim is to characterize the tumor- specific immune response induced by reconstituted tumor membranes containing purified recombinant B7 using a murine melanoma model. In specific aim 2, other murine tumors with various levels of intrinsic immunogenicity will be studied. The efficacy of experimental vaccines in treating established tumors will also be examined. The final aim of the proposal is to evaluate vaccines composed of reconstituted tumor membranes, B7, and additional immunostimulatory molecules with the goal of increasing the spectrum and intensity of tumor-specific immunity. Ultimately it may be possible to vaccinate cancer patients, within hours after surgical resection of tumor, with liposomes generated from tumor membranes, engineered to express immunostimulatory molecules by using protein transfer rather than gene transfer.